1. Field of the Invention
The invention relates generally to the image processing, and more particularly to the image processing method, the image processing apparatus and the image processing system for compressing color data.
2. Prior Art of the Invention
The color image has a huge size of data regarding colors. When the color data is displayed or transmitted, it is used to apply the method to the compression of the data size that the number of the original color data is approximated with the smaller number of colors.
A method is well known as the compressing; that is to calculate an approximated data by treating respective RGB signals (“R” means “red”, “G” means “green”, and “B” means “blue”) independently, and which is disclosed in Japanese Laid-open publication No. 61-252792, for example. The processing is explained according to FIG. 15. In FIG. 15, every color data of image information per color (the image information classified by colors included in the image data) are inputted into pre-encoder 91a, 91b and 91c, via input device 90a, 90b and 90c. The pre-encoder 91a, 91b and 91c calculate an average of data per color (the intensity of each RBG signal), and then divide a specified block of color image into two regions according to the average. In addition, the pre-encoder 91a, 91b and 91c average each data of picture elements included in the divided regions, and then calculate two representative values. According to the above processing, the block is divided into two regions per color, and two representative values are calculated per color. The combination of three colors of RGB can divide the block into 23 regions, that is to say, 8 regions, and obtain 8 colors representing each region. A post-encoder 92 detects the appearance frequency of 8 representative colors in the block, and then extracts two colors as a representative color. Those two colors are defined as a representative color in the block. Thus obtained two representative colors are inputted into an output device 93.
Besides, another method is also well known; the approximation data can be calculated by analyzing main components of RGB signals, which is disclosed in Japanese Laid-open Publication No. 01-264092, for instance. In this method, the colors (main components) representing the specific block are determined according to the correlation of the RGB signals, and according to the main components the block is divided. Therefore, the colors of the block can be approximated with specific number of representative colors.
However, the method disclosed in the Japanese Laid-open Publication No. 61-252792 has a problem that it is easy to generate a difference between the restoration image and the original because each of RGB signals is treated independently and the correlation of colors each other is not taken into consideration at all.
On the other hand, the method in the Japanese Laid-open Publication No. 01-264092 has the following problems. Since the analysis of the main components requires the multidimensional matrix calculation in order to calculate the RGB correlation, the processing volume increases. Along with the increase of the processing volume, the hardware scale such as processing circuits also gets big. Additionally, in case of the software processing with CPU and the like, the method needs much calculation time.
Moreover, in any methods described above, it is not possible to obtain the output data until all processing are completed. Accordingly, it is not possible to correspond to a case of requiring the approximation data immediately.